1. Field of the Invention
The present invention relates to a movement for on-vehicle instruments such as a speedometer, a tachometer, a water thermometer, and a fuel meter in which a rotor is angularly positioned by a current, which flows through a pair of coils in accordance with a quantity to be measured, such that the pointer mounted to the rotor indicates the magnitude of the quantity to be measured.
2. Prior Art
FIGS. 22 and 23 illustrate one such conventional movement for on-vehicle instruments.
This type of movement is referred to as a cross-coil type in which the cross-coil is formed of a first coil L1 and a second coil L2 which are wound around a bobbin B in multi-layer construction such that the two coils are positioned orthogonal to each other. A rotor Mg in the form of a permanent magnet is located in a space S within the bobbin B where the coils L1 and L2 provide a magnetic field. The rotor Mg is rotatable about a shaft R. The bobbin B is provided with terminals T at the bottom thereof for securing the bobbin B to a printed circuit board. A pointer A attached to the rotational shaft R as shown in FIGS. 24-25 cooperates with a scale plate P, thereby forming an instrument.
When a voltage Vo cos .theta. as shown in FIG. 26 is applied to the first coil L1 and a voltage Vo sin .theta. as shown in FIG. 26 is applied to the second coil L2, currents through the respective coils set up a magnetic field. The magnetic fields H1 and H2 generated by the coils L1 and L2, respectively, are orthogonal to each other as shown in FIG. 27 and produce a resultant magnetic field H. The direction of the resultant magnetic field is .theta. since the magnitudes of the respective fields H1 and H2 are proportional to Vo cos .theta. and Vo sin .theta., respectively. Therefore, when an angle is a quantity to be measured, the angular position of the resultant filed H is a direct indication of the quantity to be measured. The direction of the resultant field H is indicated by means of the pointer A mounted to the shaft R on the rotor Mg which is angularly driven by the resultant field H.
The cross coil L of the conventional movement for an instrument is constructed of a pair of coils L1 and L2 which are wound one over the other. This construction requires a bobbin B on which the coils L1 and L2 are provided and therefore the entire movement will be clumsy, causing the problem that the overall size of the movement cannot be thin enough. Since the on-vehicle instruments are generally mounted in a rather limited space such as the dash board in front of the driver, the thick and bulky structure of the conventional movements is not really space saving.